It is known that the Universal Mobile Telecommunications System (UMTS) is a third generation communication network technology that was developed by 3GPP (3rd Generation Partnership Project) to improve upon its predecessor the Global System for Mobile Communication (GSM). A UMTS network utilizes a UMTS Terrestrial Radio Access Network (UTRAN) as the air interface (radio access technology) for mobile stations accessing a UMTS network, see, e.g., 25.xxx series of 3GPP standards. A GSM network utilizes a General Packet Radio Service (GPRS) as the air interface for mobile stations accessing a GSM network, see, e.g., 23.xxx series of 3GPP standards.
Further, it is known that the Long Term Evolution (LTE) network is a 3GPP-specified network that was developed to improve upon the UMTS standard and provide an enhanced user experience and simplified technology for next generation mobile broadband. LTE radio access technology is known as Evolved UMTS Terrestrial Radio Access (E-UTRA) and the network is known as an Evolved Packet System (EPS). Details about E-UTRA may be found, by way of example, in the 36.xxx series of 3GPP standards.
Given the various network protocols and radio access technologies that are available, and given the fact that communication systems tend to be hybrid in nature (e.g., use two or more radio access technologies or network protocols) while one or more newer communication standards gradually replace one or more older communication standards, it is known that manufacturers of mobile equipment (e.g., smartphones, portable computers, etc.) design their mobile equipment with the capability to operate via multiple radio access technologies and network protocols. Thus, certain mobile equipment is known to have multi-mode capability so as to be able to selectively operate, for example, in one of two modes such as a GSM mode or an EPS mode, or, for example, in one of three modes such as a GSM mode, a UMTS mode or an EPS mode. Thus, as the mobile device roams in the communication system, it can access the system via whatever mode or modes are available in a given geographic area.
However, it has been shown that mobile equipment that operates using GSM technology can be susceptible to a so-called “man-in-the-middle” (MITM) attack. As described by Ulrike Meyer et al., “A Man-in-the-Middle Attack on UMTS,” WiSe'04, Philadelphia, Pa., October 2004, the disclosure of which is incorporated by reference herein in its entirety, the attack allows an intruder to impersonate a valid GSM base station to a UMTS subscriber operating in a GSM network regardless of the fact that UMTS authentication and key agreement is used. As such, an intruder can eavesdrop on all mobile-station-initiated traffic. This allows the intruder to obtain information from the unsuspecting user of a mobile station such as, for example, credit card information, online banking information, etc.